Skip local variant detection for remote URL images

[William-Laverty]

Summary

When an Image is initialized with a remote URL (http/https), skip the local filesystem variant detection (findVariants) that searches for @2x and ~dark alternatives in the assets directory.

Problem

As noted in #864, remote URLs already work with Image, but Ignite attempts to find local file variants for them — scanning the assets directory for density and appearance alternatives. This is unnecessary for remote images and produces warnings when the assets directory doesn't contain matching files.

Fix

• Add an isRemote flag to render(path:description:) that skips findVariants() entirely for http/https URLs.
• Detect remote URLs in markup() by checking the URL scheme.

This is a minimal, targeted change — remote images emit a clean <img> tag without triggering filesystem operations.

[MrSkwiggs]

Thanks for your contribution @William-Laverty!
I've elected to disable automatic resolution of #864 for now, as that issue was happening for an older release of Ignite.

Your changes look good to me however, so I'm happy to merge this.
We'll close #864 manually once OP gets a chance to report back.